An observation of a sample surface using a microscope normally includes a first step of taking a low-magnification image (broad-area image) with a large visual field on a sample, displaying the broad-area image on a display screen to allow an observer to search for a desired portion on the sample, and a second step of performing a magnified observation to acquire a magnified image with a smaller visual field including the desired portion, displaying the magnified image. To improve the efficiency of such operations, various techniques have been developed and proposed.
For example, Patent Document 1 discloses a technique in which a broad-area image with low magnification and a magnified image with high magnification are simultaneously displayed on the same display screen, with a rectangular frame or similar graphical element shown on the broad-area image to indicate the area corresponding to the currently shown magnified image or a previously taken magnified image. With this technique, the observer can easily grasp the positional relationship between the region of interest (ROI) and a broader area on the sample or the positional information of a previously observed or measured area.
A scanning probe microscope (SPM), which is one of the typical surface analyzers, is a device for scanning the surface of a sample with a micro-sized probe and detecting a force resulting from the interaction between the surface and the probe. This device is capable of collecting, for the same area on a sample, not only information on the altitude (surface height or surface shape) but also two-dimensional distribution data of various kinds of physical quantities, such as phase, electric current, viscoelasticity, magnetic force, surface potential or electrostatic force (see Patent Document 2). Therefore, when specifying a region of interest on the sample for the next measurement, SPM users often desire to refer to a previously obtained two-dimensional distribution data of a certain physical quantity other than the altitude, i.e. an image showing the distribution of that physical quantity.
Such a demand cannot be fully satisfied by the image-displaying method described in Patent Document 1. That is to say, the method merely provides a broad-area image showing the surface shape (altitude image) of a sample with low magnification, with a frame or similar graphical element indicating an area corresponding to a magnified image on the broad-area image. With this system, when specifying a region of interest based on a previously taken observation image showing a certain physical quantity other than the altitude, the observer must specify the region of interest by visually comparing the frame on the broad-area image and the previously taken image showing the distribution of the physical quantity concerned. Such a task of specifying a region of interest while visually comparing two or more images is cumbersome for observers and may cause an error in judgment.
Even when a broad-area image showing the altitude and a magnified observation image showing a certain physical quantity different from the altitude are simultaneously shown on the same display screen, it is difficult to know which portion on the broad-area image corresponds to the magnified observation image selected or specified by the observer. Therefore, when the user wants to observe the distribution of a certain physical quantity on a desired portion of the sample while grasping the positional relationship of a plurality of magnified observation images which were previously taken for a certain physical quantity, the task will be very time-consuming and inefficient.